Network handover method, device, and system

ABSTRACT

A network handover method is disclosed, where after UE in an LTE network requests circuit switched fallback CSFB, an MME instructs an eNB to move the UE from the LTE network to a 2G or 3G network, and requests an MSC to hand over the UE from the LTE network to a CS domain of the 2G or 3G network for the CSFB, so that the 2G or 3G network allocates a CS domain resource to the UE. After handing over to the CS domain, the UE may perform a CS domain call. By using embodiments of the present invention, an access delay is reduced when the UE accesses the CS domain of the 2G or 3G network, duration of an entire voice call is shortened, and user experience is improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.14/966,888, filed on Dec. 11, 2015, which is a continuation ofInternational Application No. PCT/CN2013/077199, filed on Jun. 13, 2013.All of the afore-mentioned patent applications are hereby incorporatedby reference in their entireties.

TECHNICAL FIELD

The present application relates to the field of communicationstechnologies, and in particular, to a network handover method, device,and system.

BACKGROUND

Universal coverage of a second generation (2G) or third generation (3G)network such as global system for mobile communications (GSM) orwideband code division multiple access (WCDMA) has basically beenimplemented.

With the development of Long Term Evolution (LTE) network technologies,the LTE network has covered some urban areas and traffic hotspot areas,and in this way, in current communications networks, the LTE networkcoexists with the 2G or 3G network.

In a calling process, user equipment (UE) may enter the 2G or 3G networkfrom the LTE network, and because bearing mechanisms of the LTE networkand the 2G or 3G network are different, the user equipment needs to handover from a packet switching (PS) domain to a circuit switching (CS)domain, and an interruption of a voice call may occur, thereby affectingcontinuity of a voice call of a user.

Circuit switched fallback (CSFB) is: when user equipment (UE) incoverage of LTE processes a voice service, the UE first returns to anetwork having a CS domain, and processes the voice service in thenetwork having a CS domain, thereby achieving an objective of providinga conventional voice service for a user in an LTE network by re-using anexisting CS domain device. In the prior art, the UE needs to hand overfrom the LTE network to a PS domain of the 2G or 3G network, or beredirected from the LTE network to the 2G or 3G network, and theninitiates a CS domain connection in the 2G or 3G network.

In the prior art, even when the UE can support a handover from the LTEnetwork to the CS domain of the 2G or 3G network, the UE also needs tomove to the PS domain of the 2G or 3G network before initiating a voicecall, thereby causing that entire voice call duration is relativelylong, and user experience is poor.

SUMMARY

For the foregoing problem in the prior art, embodiments of the presentdisclosure provide a network handover method, where in a CSFBimplementation process, UE is triggered to hand over from an LTE networkto a CS domain of a 2G or 3G network, which reduces an access delay whenthe UE accesses the CS domain of the 2G or 3G network, and also improvesuser experience. The embodiments of the present disclosure furtherprovide a corresponding device and system.

A first aspect of the present disclosure provides a network handovermethod, including:

receiving, by a mobility management entity MME, a request messageinitiated by user equipment UE located in a Long Term Evolution LTEnetwork, where the request message is used for requesting circuitswitched fallback CSFB;

sending, by the MME, a notification message to an evolved base stationeNodeB according to the request message, where the notification messageis used for instructing the eNodeB to move the UE from the LTE networkto a circuit switching CS domain of a second generation 2G or thirdgeneration 3G network for the CSFB;

receiving, by the MME, a handover required message sent by the eNodeB;and

sending, by the MME, a first handover request message to a mobileswitching center MSC, where the first handover request message is usedfor requesting the MSC to hand over the UE from the LTE network to theCS domain of the 2G or 3G network for the CSFB, so that the 2G or 3Gnetwork allocates a CS domain resource to the UE, where the CS domainresource is used for the UE to hand over from the LTE network to the CSdomain of the 2G or 3G network.

With reference to the first aspect, in a first possible implementationmanner, the notification message is further used for indicating that theLTE network, the 2G or 3G network, and the UE support handing over theUE from the LTE network to the CS domain of the 2G or 3G network for theCSFB; or, the handover required message is further used for indicatingthat the UE supports a handover from the LTE network to the CS domain ofthe 2G or 3G network.

With reference to the first aspect or the first possible implementationmanner of the first aspect, in a second possible implementation manner,the notification message includes indication information, where theindication information is used for indicating that the LTE network, the2G or 3G network, and the UE support handing over the UE from the LTEnetwork to the CS domain of the 2G or 3G network for the CSFB.

With reference to the second possible implementation manner of the firstaspect, in a third possible implementation manner, the indicationinformation is used for indicating that the LTE network, the 2G or 3Gnetwork, and the UE support a single radio voice call continuity SRVCChandover.

With reference to the first aspect, or any one of the first to the thirdpossible implementation manners of the first aspect, in a fourthpossible implementation manner, the method further includes:

determining, by the MME, that the LTE network and the 2G or 3G networksupport handing over the UE from the LTE network to the CS domain of the2G or 3G network for the CSFB, and that the UE supports a handover fromthe LTE network to the CS domain of the 2G or 3G network.

With reference to the first aspect, or any one of the first to thefourth possible implementation manners of the first aspect, in a fifthpossible implementation manner, the method further includes:

receiving, by the MME, a first handover response message that is sent bythe MSC in response to the first handover request message, where thefirst handover response message includes information about a CS domainwireless resource allocated to the UE by a base station in the 2G or 3Gnetwork; and sending, by the MME, a handover required response messageto the eNodeB, where the handover required response message includes theinformation about the CS domain wireless resource, and the informationabout the CS domain wireless resource is used for the UE to hand overfrom the LTE network to the CS domain of the 2G or 3G network for theCSFB.

With reference to the first aspect, or any one of the first to the fifthpossible implementation manners of the first aspect, in a sixth possibleimplementation manner, the handover required message is a handoverrequired message of a handover from the LTE network to a packetswitching PS domain of the 2G or 3G network, or a handover requiredmessage of a handover from the LTE network to the CS domain of the 2G or3G network.

With reference to the first aspect, or any one of the first to the fifthpossible implementation manners of the first aspect, in a seventhpossible implementation manner, the handover required message is ahandover required message of a handover from the LTE network to a PSdomain and the CS domain of the 2G or 3G network.

With reference to the seventh possible implementation manner of thefirst aspect, in an eighth possible implementation manner, the methodfurther includes:

sending, by the MME, a second handover request message to a servinggeneral packet radio service support node SGSN, where the secondhandover request message is used for requesting the SGSN to initiate ahandover from the LTE network to the PS domain of the 2G or 3G network.

A second aspect of the present disclosure provides a network handovermethod, including:

receiving, by an evolved base station eNodeB located in a Long TermEvolution LTE network, a notification message sent by a mobilitymanagement entity MME, where the notification message is used forinstructing the eNodeB to move user equipment from the LTE network to acircuit switching CS domain of a 2G or 3G network for circuit switchedfallback CSFB;

sending, by the eNodeB, a handover required message to the MME;

receiving, by the eNodeB, a handover required response message sent bythe MME, where the handover required response message includesinformation about a CS domain wireless resource, and the informationabout the CS domain wireless resource is used for the UE to hand overfrom the LTE network to the CS domain of the 2G or 3G network; andsending, by the eNodeB, a handover command to the UE, where the handovercommand is used for instructing the UE to hand over from the LTE networkto the CS domain of the 2G or 3G network, and the handover commandincludes the information about the CS domain wireless resource.

With reference to the second aspect, in a first possible implementationmanner,

the notification message is further used for indicating that the LTEnetwork, the 2G or 3G network, and the UE support handing over the UEfrom the LTE network to the CS domain of the 2G or 3G network for theCSFB; or,

the handover command is used for instructing the UE to hand over fromthe LTE network to the circuit switching CS domain of the 2G or 3Gnetwork for the CSFB.

With reference to the second aspect, or the first possibleimplementation manner of the second aspect, in a third possibleimplementation manner, the method further includes:

determining, by the eNodeB, that the UE supports a handover from the LTEnetwork to the CS domain of the 2G or 3G network.

With reference to the second aspect, or the first or second possibleimplementation manner of the second aspect, in a third possibleimplementation manner,

the handover required message includes first indication information,where the first indication information is used for requesting the MME tohand over the UE from the LTE network to the CS domain of the 2G or 3Gnetwork for the CSFB;

or, the first indication information is used for requesting the MME tohand over the UE from the LTE network to the CS domain of the 2G or 3Gnetwork for the CSFB, and indicating that the UE supports a handoverfrom the LTE network to the CS domain of the 2G or 3G network;

or, the handover required message includes a source to targettransparent container, where the source to target transparent containerincludes second indication information, and the second indicationinformation is used for requesting a base station in the 2G or 3Gnetwork to hand over the UE from the LTE network to the CS domain of the2G or 3G network for the CSFB.

With reference to the third possible implementation manner of the secondaspect, in a fourth possible implementation manner, the secondindication information is further used for indicating that the UEsupports a handover from the LTE network to the CS domain of the 2G or3G network.

With reference to the second aspect, or any one of the first to thefourth possible implementation manners of the second aspect, in a fifthpossible implementation manner,

the handover required message is a handover required message of ahandover from the LTE network to a packet switching PS domain of the 2Gor 3G network, or a handover required message of a handover from the LTEnetwork to the CS domain of the 2G or 3G network.

With reference to the second aspect, or any one of the first to thefourth possible implementation manners of the second aspect, in a sixthpossible implementation manner,

the handover required message is a handover required message of ahandover from the LTE network to a PS domain and the CS domain of the 2Gor 3G network.

With reference to the sixth possible implementation manner of the secondaspect, in a seventh possible implementation manner,

determining, by the eNodeB, that the UE supports a handover from the LTEnetwork to the PS domain of the 2G or 3G network, where

the handover command is further used for instructing the UE to hand overfrom the LTE network to the PS domain of the 2G or 3G network, thehandover command includes information about a PS domain resource of the2G or 3G network, and the information about the PS domain resource isused for the UE to hand over from the LTE network to the PS domain ofthe 2G or 3G network.

A third aspect of the present disclosure provides a network handovermethod, including:

receiving, by a mobile switching center MSC, a first handover requestmessage sent by a mobility management entity MME, where the firsthandover request message is used for requesting the MSC to hand overuser equipment UE from a Long Term Evolution LTE network to a circuitswitching CS domain of a second generation 2G or third generation 3Gnetwork for circuit switched fallback CSFB;

sending, by the MSC, a third handover request message to a base stationin the 2G or 3G network, where the third handover request message isused for requesting the base station to allocate a CS domain resource tothe UE for handing over to the CS domain of the 2G or 3G network;

receiving, by the MSC, a third handover request response message sent bythe base station, where the third handover request response messageincludes information about a CS domain wireless resource that isallocated by the base station to the UE for handing over to the CSdomain of the 2G or 3G network;

sending, by the MSC, a first handover response message to the MME, wherethe first handover response message includes the information about theCS domain wireless resource; and

receiving, by the MSC, a handover completion message sent by the UE,where the handover completion message is used for indicating that the UEcompletes handing over from the LTE network to the CS domain of the 2Gor 3G network.

With reference to the third aspect, in a first possible implementationmanner, the first handover request message is further used forindicating that the UE supports a handover from the LTE network to theCS domain of the 2G or 3G network.

With reference to the third aspect, or the first possible implementationmanner of the third aspect, in a second possible implementation manner,the method further includes: receiving, by the MSC, a first CS callconnection setup request message sent by the UE, where the first CS callconnection setup request message is used for requesting the MSC togenerate a first session.

With reference to the third aspect, or the first possible implementationmanner of the third aspect, in a third possible implementation manner,the method further includes:

sending, by the MSC, a second CS call connection setup request messageto the UE, where the second CS call connection setup request message isused for requesting the UE to generate a second session.

With reference to the first possible implementation manner of the thirdaspect, in a fourth possible implementation manner, the method furtherincludes:

after receiving the first CS call connection setup request message,sending, by the MSC, a session release message to the UE, where thesession release message is used for requesting the UE to release a thirdsession that is generated by the UE in a process of handing over fromthe LTE network to the CS domain of the 2G or 3G network.

With reference to the second possible implementation manner of the thirdaspect, in a fifth possible implementation manner, the method furtherincludes:

after receiving a call confirmation message responding to the second CScall connection setup request message, sending, by the MSC, a sessionrelease message to the UE, where the session release message is used forrequesting the UE to release a third session that is generated by the UEin a process of handing over from the LTE network to the CS domain ofthe 2G or 3G network.

A fourth aspect of the present disclosure provides a network handovermethod, including:

sending, by user equipment UE located in a Long Term Evolution LTEnetwork, a request message to a mobility management entity MME, wherethe request message is used for requesting circuit switched fallbackCSFB;

receiving, by the UE, a handover command sent by an evolved base stationeNodeB, where the handover command is used for instructing the UE tohand over from the LTE network to a circuit switching CS domain of a 2Gor 3G network for the CSFB, and the handover command includesinformation about a CS domain wireless resource that is allocated by the2G or 3G network to the UE for handing over from the LTE network to theCS domain of the 2G or 3G network; and

handing over, by the UE, from the LTE network to the CS domain of the 2Gor 3G network according to the handover command.

With reference to the fourth aspect, in a first possible implementationmanner, the method further includes:

sending, in the CS domain of the 2G or 3G network by the UE, a CS callconnection setup request message to a mobile switching center MSC, wherethe CS call connection setup request message is used for requesting theMSC to generate a first session.

With reference to the fourth aspect, in a second possible implementationmanner, the method further includes: receiving, in the CS domain of the2G or 3G network by the UE, a CS call connection setup request messagesent by the MSC, where the CS call connection setup request message isused for requesting the UE to generate a second session.

With reference to the fourth aspect, or the first or the second possibleimplementation manner of the fourth aspect, in a third possibleimplementation manner, the method further includes:

receiving, by the UE, a session release message sent by the MSC, wherethe session release message is used for instructing the UE to release athird session that is generated by the UE in a process of handing overfrom the LTE network to the CS domain of the 2G or 3G network.

With reference to the fourth aspect, or any one of the first to thethird possible implementation manners of the fourth aspect, in a fourthpossible implementation manner, the handover command further includesinformation about a PS domain wireless resource that is allocated by the2G or 3G network to the UE for handing over from the LTE network to apacket switching PS domain of the 2G or 3G network.

A fifth aspect of the present disclosure provides a network handovermethod, including:

receiving, by a base station in a 2G or 3G network, a third handoverrequest message sent by a mobile switching center MSC, where the thirdhandover request message is used for requesting the base station to handover user equipment UE from a Long Term Evolution LTE network to acircuit switching CS domain of the 2G or 3G network for circuit switchedfallback CSFB;

sending, by the base station, a third handover request response messageto the MSC, where the third handover request response message includesinformation about a CS domain wireless resource, and the informationabout the CS domain wireless resource is used for the UE to hand overfrom the LTE network to the CS domain of the 2G or 3G network; and

receiving, by the base station, a handover completion message sent bythe UE, where the handover completion message is used for indicatingthat the UE completes handing over from the LTE network to the CS domainof the 2G or 3G network.

With reference to the fifth aspect, in a first possible implementationmanner, the third handover request message includes indicationinformation, where the indication information is used for requesting thebase station to hand over the UE from the LTE network to the CS domainof the 2G or 3G network for the CSFB;

and/or, the indication information is used for indicating that the UEsupports a handover from the LTE network to the CS domain of the 2G or3G network.

With reference to the first possible implementation manner of the fifthaspect, in a second possible implementation manner,

the third handover request message includes a source to targettransparent container, and the source to target transparent containerincludes the indication information.

With reference to the fifth aspect, or the first or the second possibleimplementation manner of the fifth aspect, in a third possibleimplementation manner, the method further includes: after receiving thehandover completion message,

sending, by the base station, Universal Mobile Telecommunications Systemterrestrial radio access network UTRAN mobility information to the UE,where the UTRAN mobility information does not include a location domainidentity LAI, and after a predetermined time, sending, by the basestation, the LAI to the UE;

or, sending, by the base station, UTRAN mobility information to the UE,where the UTRAN mobility information does not include an LAI, and afterreceiving a call release message or call connection completion messagesent by the MSC or a call connection completion message sent by the UE,sending, by the base station, the LAI to the UE.

With reference to the fifth aspect, or the first or the second possibleimplementation manner of the fifth aspect, in a fourth possibleimplementation manner, the method further includes:

receiving, by the base station, a location update request message sentby the UE, and determining, by the base station, to skip sending thelocation update request message to the MSC; and

sending, by the base station, a location update acceptation message tothe UE.

With reference to the fifth aspect, or the first or the second possibleimplementation manner of the fifth aspect, in a fifth possibleimplementation manner, the method further includes:

receiving, by the base station, a call release message sent by the MSC,where the call release message is an Iu interface release command or aclear command; and

redirecting, by the base station, the UE to the LTE network, or, handingover, by the base station, the UE to the LTE network.

A sixth aspect of the present disclosure provides a mobility managemententity, including:

a receiving unit, configured to receive a request message initiated byuser equipment UE located in a Long Term Evolution LTE network, wherethe request message is used for requesting circuit switched fallbackCSFB;

a generating unit, configured to generate a notification messageaccording to the request message received by the receiving unit, wherethe notification message is used for instructing an evolved base stationeNodeB to move the UE from the LTE network to a circuit switching CSdomain of a second generation 2G or third generation 3G network for theCSFB; and

a sending unit, configured to send the notification message generated bythe generating unit to the eNodeB, where

the receiving unit is further configured to receive a handover requiredmessage sent by the eNodeB;

the generating unit is further configured to generate a first handoverrequest message according to the handover required message received bythe receiving unit, where the first handover request message is used forrequesting an MSC to hand over the UE from the LTE network to the CSdomain of the 2G or 3G network for the CSFB; and

the sending unit is further configured to send the first handoverrequest message generated by the generating unit to the mobile switchingcenter MSC, so that the 2G or 3G network allocates a CS domain resourceto the UE, where the CS domain resource is used for the UE to hand overfrom the LTE network to the CS domain of the 2G or 3G network.

With reference to the sixth aspect, in a first possible implementationmanner,

the notification message is further used for indicating that the LTEnetwork, the 2G or 3G network, and the UE support handing over the UEfrom the LTE network to the CS domain of the 2G or 3G network for theCSFB; or,

the handover required message includes first indication information,where the first indication information is used for requesting the MME tohand over the UE from the LTE network to the CS domain of the 2G or 3Gnetwork for the CSFB;

or, the first indication information is used for requesting the MME tohand over the UE from the LTE network to the CS domain of the 2G or 3Gnetwork for the CSFB, and indicating that the UE supports a handoverfrom the LTE network to the CS domain of the 2G or 3G network.

With reference to the sixth aspect or the first possible implementationmanner of the sixth aspect, in a second possible implementation manner,

the notification message includes indication information, where theindication information is used for indicating that the LTE network, the2G or 3G network, and the UE support handing over the UE from the LTEnetwork to the CS domain of the 2G or 3G network for the CSFB.

With reference to the second possible implementation manner of the sixthaspect, in a third possible implementation manner,

the indication information is used for indicating that the LTE network,the 2G or 3G network, and the UE support a single radio voice callcontinuity SRVCC handover.

With reference to the sixth aspect, or any one of the first to the thirdpossible implementation manners of the sixth aspect, in a fourthpossible implementation manner, the mobility management entity furtherincludes:

a determining unit, configured to determine that the LTE network and the2G or 3G network support handing over the UE from the LTE network to theCS domain of the 2G or 3G network for the CSFB, and that the UE supportsa handover from the LTE network to the CS domain of the 2G or 3Gnetwork.

With reference to the sixth aspect, or any one of the first to thefourth possible implementation manners of the sixth aspect, in a fifthpossible implementation manner,

the receiving unit is further configured to receive a first handoverresponse message that is sent by the MSC in response to the firsthandover request message, where the first handover response messageincludes information about a CS domain wireless resource allocated tothe UE by a base station in the 2G or 3G network; and

the generating unit is further configured to generate a handoverrequired response message according to the handover required messagereceived by the receiving unit, where the handover required responsemessage includes the information about the CS domain wireless resource,and the information about the CS domain wireless resource is used forthe UE to hand over from the LTE network to the CS domain of the 2G or3G network for the CSFB; and the sending unit is further configured tosend the handover required response message generated by the generatingunit to the eNodeB, where the handover required response messageincludes the information about the CS domain wireless resource, and theinformation about the CS domain wireless resource is used for the UE tohand over from the LTE network to the CS domain of the 2G or 3G networkfor the CSFB.

With reference to the sixth aspect, or any one of the first to the fifthpossible implementation manners of the sixth aspect, in a sixth possibleimplementation manner, the handover required message is a handoverrequired message of a handover from the LTE network to a packetswitching PS domain of the 2G or 3G network, or a handover requiredmessage of a handover from the LTE network to the CS domain of the 2G or3G network.

With reference to the sixth aspect, or any one of the first to the fifthpossible implementation manners of the sixth aspect, in a seventhpossible implementation manner, the handover required message is ahandover required message of a handover from the LTE network to a PSdomain and the CS domain of the 2G or 3G network.

With reference to the seventh possible implementation manner of thesixth aspect, in an eighth possible implementation manner, the sendingunit is further configured to send a second handover request message toa serving general packet radio service support node SGSN, where thesecond handover request message is used for requesting the SGSN toinitiate a handover from the LTE network to the PS domain of the 2G or3G network.

A seventh aspect of the present disclosure provides an evolved basestation eNodeB, including:

a receiving unit, configured to receive a notification message sent by amobility management entity MME, where the notification message is usedfor instructing the eNodeB to move user equipment UE from a Long TermEvolution LTE network to a circuit switching CS domain of a 2G or 3Gnetwork for circuit switched fallback CSFB;

a generating unit, configured to generate a handover required messageaccording to the notification message received by the receiving unit;and

a sending unit, configured to send the handover required messagegenerated by the generating unit to the MME, where

the receiving unit is further configured to receive a handover requiredresponse message sent by the MME, where the handover required responsemessage includes information about a CS domain wireless resource, andthe information about the CS domain wireless resource is used for the UEto hand over from the LTE network to the CS domain of the 2G or 3Gnetwork;

the generating unit is further configured to generate a handover commandaccording to the handover required response message received by thereceiving unit, where the handover command is used for instructing theUE to hand over from the LTE network to the CS domain of the 2G or 3Gnetwork, and the handover command includes the information about the CSdomain wireless resource; and

the sending unit is further configured to send the handover commandgenerated by the generating unit to the UE.

With reference to the seventh aspect, in a first possible implementationmanner,

the notification message is further used for indicating that the LTEnetwork, the 2G or 3G network, and the UE support handing over the UEfrom the LTE network to the CS domain of the 2G or 3G network for theCSFB; or,

the handover command is used for instructing the UE to hand over fromthe LTE network to the circuit switching CS domain of the 2G or 3Gnetwork for the CSFB.

With reference to the seventh aspect, or the first possibleimplementation manner of the seventh aspect, in a third possibleimplementation manner, the evolved base station further includes:

a first determining unit, configured to determine that the UE supports ahandover from the LTE network to the CS domain of the 2G or 3G network.

With reference to the seventh aspect, or the first or second possibleimplementation manner of the seventh aspect, in a third possibleimplementation manner,

the handover required message includes first indication information,where the first indication information is used for requesting the MME tohand over the UE from the LTE network to the CS domain of the 2G or 3Gnetwork for the CSFB;

or, the first indication information is used for requesting the MME tohand over the UE from the LTE network to the CS domain of the 2G or 3Gnetwork for the CSFB, and indicating that the UE supports a handoverfrom the LTE network to the CS domain of the 2G or 3G network;

or, the handover required message includes a source to targettransparent container, where the source to target transparent containerincludes second indication information, and the second indicationinformation is used for requesting a base station in the 2G or 3Gnetwork to hand over the UE from the LTE network to the CS domain of the2G or 3G network for the CSFB.

With reference to the third possible implementation manner of theseventh aspect, in a fourth possible implementation manner, the secondindication information is further used for indicating that the UEsupports a handover from the LTE network to the CS domain of the 2G or3G network.

With reference to the seventh aspect, or any one of the first to thefourth possible implementation manners of the seventh aspect, in a fifthpossible implementation manner,

the handover required message is a handover required message of ahandover from the LTE network to a packet switching PS domain of the 2Gor 3G network, or a handover required message of a handover from the LTEnetwork to the CS domain of the 2G or 3G network.

With reference to the seventh aspect, or any one of the first to thefourth possible implementation manners of the seventh aspect, in a sixthpossible implementation manner,

the handover required message is a handover required message of ahandover from the LTE network to a PS domain and the CS domain of the 2Gor 3G network.

With reference to the sixth possible implementation manner of theseventh aspect, in a seventh possible implementation manner,

the evolved base station further includes:

a second determining unit, configured to determine that the UE supportsa handover from the LTE network to the PS domain of the 2G or 3Gnetwork, where

the handover command is further used for instructing the UE to hand overfrom the LTE network to the PS domain of the 2G or 3G network, thehandover command includes information about a PS domain resource of the2G or 3G network, and the information about the PS domain resource isused for the UE to hand over from the LTE network to the PS domain ofthe 2G or 3G network.

An eighth aspect of the present disclosure provides a mobile switchingcenter MSC, including:

a receiving unit, configured to receive a first handover request messagesent by a mobility management entity MME, where the first handoverrequest message is used for requesting the MSC to hand over userequipment UE from a Long Term Evolution LTE network to a circuitswitching CS domain of a second generation 2G or third generation 3Gnetwork for circuit switched fallback CSFB;

a generating unit, configured to generate a third handover requestmessage according to the first handover request message received by thereceiving unit, where the third handover request message is used forrequesting a base station in the 2G or 3G network to allocate a CSdomain resource to the UE for handing over to the CS domain of the 2G or3G network; and

a sending unit, configured to send the third handover request messagegenerated by the generating unit to the base station, where

the receiving unit is further configured to receive a third handoverrequest response message sent by the base station, where the thirdhandover request response message includes information about a CS domainwireless resource that is allocated by the base station to the UE forhanding over to the CS domain of the 2G or 3G network;

the generating unit is further configured to generate a first handoverresponse message according to the first handover request messagereceived by the receiving unit, where the first handover responsemessage includes the information about the CS domain wireless resource;

the sending unit is further configured to send the first handoverresponse message generated by the generating unit to the MME; and

the receiving unit is further configured to receive a handovercompletion message sent by the UE, where the handover completion messageis used for indicating that the UE completes handing over from the LTEnetwork to the CS domain of the 2G or 3G network.

With reference to the eighth aspect, in a first possible implementationmanner, the first handover request message is further used forindicating that the UE supports a handover from the LTE network to theCS domain of the 2G or 3G network.

With reference to the eighth aspect, or the first possibleimplementation manner of the eighth aspect, in a second possibleimplementation manner, the receiving unit is further configured toreceive a first CS call connection setup request message sent by the UE,where the first CS call connection setup request message is used forrequesting the MSC to generate a first session.

With reference to the eighth aspect, or the first possibleimplementation manner of the eighth aspect, in a third possibleimplementation manner, the sending unit is further configured to send asecond CS call connection setup request message to the UE, where thesecond CS call connection setup request message is used for requestingthe UE to generate a second session.

With reference to the second possible implementation manner of theeighth aspect, in a fourth possible implementation manner, the sendingunit is further configured to: after the receiving unit receives thefirst CS call connection setup request message, send a session releasemessage to the UE, where the session release message is used forrequesting the UE to release a third session that is generated by the UEin a process of handing over from the LTE network to the CS domain ofthe 2G or 3G network.

With reference to the third possible implementation manner of the eighthaspect, in a fifth possible implementation manner, the sending unit isfurther configured to: after the receiving unit receives a callconfirmation message, send a session release message to the UE, wherethe session release message is used for requesting the UE to release athird session that is generated by the UE in a process of handing overfrom the LTE network to the CS domain of the 2G or 3G network.

A ninth aspect of the present disclosure provides user equipment,including:

a sending unit, configured to send a request message to a mobilitymanagement entity MME, where the request message is used for requestingcircuit switched fallback CSFB;

a receiving unit, configured to receive a handover command sent by anevolved base station eNodeB, where the handover command is used forinstructing the UE to hand over from a Long Term Evolution LTE networkto a circuit switching CS domain of a 2G or 3G network for the CSFB, andthe handover command includes information about a CS domain wirelessresource that is allocated by the 2G or 3G network to the UE for handingover from the LTE network to the CS domain of the 2G or 3G network; and

a handover unit, configured to hand over from the LTE network to the CSdomain of the 2G or 3G network according to the handover commandreceived by the receiving unit.

With reference to the ninth aspect, in a first possible implementationmanner, the sending unit is further configured to send, in the CS domainof the 2G or 3G network, a first CS call connection setup requestmessage to a mobile switching center MSC, where the first CS callconnection setup request message is used for requesting the MSC togenerate a first session.

With reference to the ninth aspect, in a second possible implementationmanner, the receiving unit is further configured to receive, in the CSdomain of the 2G or 3G network, a second CS call connection setuprequest message sent by a mobile switching center MSC, where the secondCS call connection setup request message is used for requesting the UEto generate a second session.

With reference to the ninth aspect, or the first possible implementationof the ninth aspect, in a third possible implementation manner, thereceiving unit is further configured to receive a session releasemessage sent by the MSC, where the session release message is used forinstructing the UE to release a third session that is generated by theUE in a process of handing over from the LTE network to the CS domain ofthe 2G or 3G network.

With reference to the ninth aspect, or any one of the first to the thirdpossible implementation manners of the ninth aspect, in a fourthpossible implementation manner, the handover command further includesinformation about a PS domain wireless resource that is allocated by the2G or 3G network to the UE for handing over from the LTE network to apacket switching PS domain of the 2G or 3G network.

A tenth aspect of the present disclosure provides a base station in asecond generation 2G or third generation 3G network, including:

a receiving unit, configured to receive a third handover request messagesent by a mobile switching center MSC, where the third handover requestmessage is used for requesting the base station to hand over userequipment UE from a Long Term Evolution LTE network to a circuitswitching CS domain of the 2G or 3G network for circuit switchedfallback CSFB;

a generating unit, configured to generate a third handover requestresponse message according to the third handover request messagereceived by the receiving unit, where the third handover requestresponse message includes information about a CS domain wirelessresource, and the information about the CS domain wireless resource isused for the UE to hand over from the LTE network to the CS domain ofthe 2G or 3G network; and

a sending unit, configured to send the third handover request responsemessage generated by the generating unit to the MSC, where

the receiving unit is further configured to receive a handovercompletion message sent by the UE, where the handover completion messageis used for indicating that the UE completes handing over from the LTEnetwork to the CS domain of the 2G or 3G network.

With reference to the tenth aspect, in a first possible implementationmanner, the handover request message includes indication information,where the indication information is used for requesting the base stationto hand over the UE from the LTE network to the CS domain of the 2G or3G network for the CSFB;

and/or, the indication information is used for indicating that the UEsupports a handover from the LTE network to the CS domain of the 2G or3G network.

With reference to the first possible implementation manner of the tenthaspect, in a second possible implementation manner,

the handover request message includes a source to target transparentcontainer, and the source to target transparent container includes theindication information.

With reference to the tenth aspect, or the first or the second possibleimplementation manner of the tenth aspect, in a third possibleimplementation manner, the sending unit is further configured to sendUniversal Mobile Telecommunications System terrestrial radio accessnetwork UTRAN mobility information to the UE, where the UTRAN mobilityinformation does not include a location domain identity LAI, and after apredetermined time, send the LAI to the UE.

With reference to the tenth aspect, or the first or the second possibleimplementation manner of the tenth aspect, in a fourth possibleimplementation manner, the sending unit is further configured to sendUniversal Mobile Telecommunications System terrestrial radio accessnetwork UTRAN mobility information to the UE, where the UTRAN mobilityinformation does not include a location domain identity LAI;

the receiving unit is further configured to receive a call releasecommand or call connection completion message sent by the MSC or a callconnection completion message sent by the UE; and

the sending unit is further configured to send the LAI to the UE afterthe receiving unit receives the call release command or the callconnection completion message.

With reference to the tenth aspect, or the first or the second possibleimplementation manner of the tenth aspect, in a fifth possibleimplementation manner, the receiving unit is further configured toreceive a location update request message sent by the UE, and determineto skip sending the location update request message to the MSC; and

the sending unit is further configured to send a location updateacceptation message to the UE after the receiving unit receives thelocation update request message.

With reference to the tenth aspect, or the first or the second possibleimplementation manner of the tenth aspect, in a sixth possibleimplementation manner, the receiving unit is further configured toreceive a call release message sent by the MSC, where the call releasemessage is an Iu interface release command or a clear command; and

the base station further includes a redirection unit or a handover unit,where

the redirection unit is configured to redirect the UE to the LTE networkaccording to the call release message received by the receiving unit;and

the handover unit is configured to hand over the UE to the LTE networkaccording to the call release message received by the receiving unit.

An eleventh aspect of the present disclosure provides a network handoversystem, including a mobility management entity, a base station, a mobileswitching center, a base station, and user equipment, where

the mobility management entity is the mobility management entitydescribed in the foregoing technical solutions;

the evolved base station is the evolved base station described in theforegoing technical solutions;

the mobile switching center is the mobile switching center described inthe foregoing technical solutions;

the user equipment is the user equipment described in the foregoingtechnical solutions; and

the base station is the base station described in the foregoingtechnical solutions.

In the embodiments of the present disclosure, in a circuit switchedfallback implementation process, a handover from an LTE network to a 2Gor 3G network is triggered, so that UE can directly hand over from theLTE network to a CS domain of the 2G or 3G network. In this way, aresource may be allocated on a network side to the UE for handing overfrom the LTE to the CS domain of the 2G or 3G network, which avoids thata CS domain resource is allocated for the CSFB after the UE hands overfrom the LTE network to a PS domain of the 2G or 3G network or isredirected to the 2G or 3G network, thereby reducing an access delaywhen the UE accesses the CS domain of the 2G or 3G network, shorteningentire voice call duration, and improving user experience.

BRIEF DESCRIPTION OF DRAWINGS

To describe the technical solutions in the embodiments of the presentdisclosure more clearly, the following briefly introduces theaccompanying drawings required for describing the embodiments.Apparently, the accompanying drawings in the following description showmerely some embodiments of the present disclosure, and a person skilledin the art may still derive other drawings from these accompanyingdrawings without creative efforts.

FIG. 1 is a schematic diagram of an embodiment of a network handovermethod according to an embodiment of the present disclosure;

FIG. 2 is a schematic diagram of another embodiment of a networkhandover method according to an embodiment of the present disclosure;

FIG. 3 is a schematic diagram of another embodiment of a networkhandover method according to an embodiment of the present disclosure;

FIG. 4 is a schematic diagram of another embodiment of a networkhandover method according to an embodiment of the present disclosure;

FIG. 5 is a schematic diagram of another embodiment of a networkhandover method according to an embodiment of the present disclosure;

FIG. 6 is a schematic diagram of an embodiment of a network handovermethod according to an embodiment of the present disclosure;

FIG. 7 is a schematic diagram of an embodiment of a network handovermethod according to an embodiment of the present disclosure;

FIG. 8 is a schematic diagram of an embodiment of a mobility managemententity according to an embodiment of the present disclosure;

FIG. 9 is a schematic diagram of an embodiment of an evolved basestation according to an embodiment of the present disclosure;

FIG. 10 is a schematic diagram of an embodiment of a mobile switchingcenter according to an embodiment of the present disclosure;

FIG. 11 is a schematic diagram of an embodiment of user equipmentaccording to an embodiment of the present disclosure;

FIG. 12 is a schematic diagram of an embodiment of a base station in a2G or 3G network according to an embodiment of the present disclosure;and

FIG. 13 is a schematic diagram of an embodiment of a system according toan embodiment of the present disclosure.

DESCRIPTION OF EMBODIMENTS

Embodiments of the present disclosure provide a network handover method,where in a circuit switched fallback implementation process, UE istriggered to hand over from an LTE network to a CS domain of a 2G or 3Gnetwork, which reduces an access delay when the UE accesses the CSdomain of the 2G or 3G network, and also improves user experience. Theembodiments of the present disclosure further provide a correspondingdevice and system. The following gives detailed descriptions.

Full names and abbreviations of some communications terms involved inthe embodiments of the present disclosure include: a mobility managemententity (MME), an evolved base station (eNodeB), user equipment (UE), amobile switching center (MSC), a second generation or third generationmobile communications technology (2G or 3G), a base station (BS), wherethe base station in the embodiments of the present disclosure include abase station controller (BSC) and a radio network controller (RNC), LongTerm Evolution (LTE), a serving GPRS support node (SGSN), circuitswitched fallback (CSFB), terrestrial radio access network (UTRAN),global system for mobile communications (GSM), enhanced data rates forGSM evolution (EDGE), and global system for mobilecommunications/enhanced data rates for GSM evolution radio accessnetwork (GERAN).

First, second, third, fourth, and fifth in the embodiments of thepresent disclosure are only used for distinguishing different indicationinformation, messages, or other objects, and do not represent a sequencerelationship.

The following clearly describes the technical solutions in theembodiments of the present disclosure with reference to the accompanyingdrawings in the embodiments of the present disclosure. Apparently, thedescribed embodiments are merely some but not all of the embodiments ofthe present disclosure. All other embodiments obtained by a personskilled in the art based on the embodiments of the present disclosurewithout creative efforts shall fall within the protection scope of thepresent disclosure.

Referring to FIG. 1, FIG. 1 shows a fallback process implemented by UEby handing over from an LTE network to a 2G or 3G network and a callingprocess after the handover.

S100: UE sends an extended service request to an MME, where the extendedservice request is used for requesting circuit switched fallback CSFB.

S100 a: The MME may determine whether an LTE network and a 2/3G networksupport handing over the UE from the LTE network to a CS domain of the2G or 3G network for the CSFB.

The MME may also not perform the determining, and instead, considers bydefault that a communications network supports handing over the UE fromthe LTE network to the CS domain of the 2G or 3G network for the CSFB,or only performs determining on some networks.

The communications network is the LTE network and the 2G or 3G network.

S5105: The MME sends a notification message to an evolved base stationeNodeB according to the extended service request, where the notificationmessage is used for instructing the eNodeB to move the UE from the LTEnetwork to the CS domain of the 2G or 3G network for the CSFB, that is,the notification message is used for indicating to the eNB that the UEshould be moved to the 2G or 3G network for the CSFB.

When the MME determines that the LTE network and the 2G or 3G networksupport handing over the UE from the LTE network to the CS domain of the2G or 3G network for the CSFB, the MME may notify, by sending thenotification message, the eNodeB of whether the LTE network and the 2Gor 3G network support handing over the UE from the LTE network to the CSdomain of the 2G or 3G network for the CSFB, so that the eNodeBinitiates a handover required of handing over the UE from the LTEnetwork to the CS domain of the 2G or 3G network for the CSFB.

For example, the notification message may include indicationinformation, where the indication information is used for indicatingthat the communications network and the UE support handing over the UEfrom the LTE network to the CS domain of the 2G or 3G network for theCSFB.

For example, the indication information may be indication information ofa single radio voice call continuity (SRVCC) handover, and is used forindicating that the LTE network and the 2G/3G network support handingover the UE from the LTE network to the 2G or 3G network for the CSFB.

The indication information in the embodiments of the present disclosuremaybe referred to as an optimized CSFB indicator, a SRVCC based CSFBindicator, an enhanced CSFB indicator, or an enhanced CSFB possibleindicator, or an SRVCC operation possible indicator.

S5110: The eNodeB sends a handover required message to the MME.

The handover required message may be a handover required message of ahandover from the LTE network to a packet switching PS domain of the 2Gor 3G network (for example, an LTE to 2/3G PS HO Required message), or ahandover required message of a handover from the LTE network to the CSdomain of the 2G or 3G network (for example, an LTE to 2/3G SRVCC HORequired message), or a handover required message of a handover from theLTE network to a PS domain and the CS domain of the 2G or 3G network(for example, an LTE to 2/3G SRVCC and PS HO Required message).

The handover required message may include capability information of theUE, which is used for indicating frequency band information, an accesscapability, and the like supported by the UE. For example, thecapability information of the UE may be at least one of a class mark 2(classmark2) and a class mark 3 (classmark3). In the prior art, when theUE does not support a CS handover from the LTE network to the 2G/3Gnetwork, the eNodeB may not send the capability information of the UE tothe MME; therefore, the MME does not have the capability information ofthe UE. After acquiring the capability information of the UE, the MMEmay send the capability information of the UE to an MSC, so that the MSCcan execute the handover to the 2G/3G CS. In this embodiment of thepresent disclosure, the capability information of the UE may betransferred to the MME by using a handover required message.

The handover required message includes first indication information,where the first indication information is used for requesting the MME tohand over the UE from the LTE network to the CS domain of the 2G or 3Gnetwork for the CSFB;

or, the first indication information is used for requesting the MME tohand over the UE from the LTE network to the CS domain of the 2G or 3Gnetwork for the CSFB, and indicating that the UE supports a handoverfrom the LTE network to the CS domain of the 2G or 3G network;

or, the handover required message includes a source to targettransparent container, where the source to target transparent containerincludes second indication information, and the second indicationinformation is used for requesting a base station in the 2G or 3Gnetwork to hand over the UE from the LTE network to the CS domain of the2G or 3G network for the CSFB.

The first indication information may be referred to as a CSFB indicator,an optimized CSFB indicator, an SRVCC based CSFB indicator, an enhancedCSFB indicator, or an enhanced CSFB possible indicator.

When the second indication information does not indicate that the UEsupports a handover from the LTE network to the CS domain of the 2G or3G network, the MME may consider by default that the UE supports thehandover. When the first indication information does not indicate thatthe UE supports a handover from the LTE network to the CS domain of the2G or 3G network, the base station in the 2/3G network may consider bydefault that the UE supports the handover. The second indicationinformation and the first indication information each may be referred toas a CSFB indicator, an optimized CSFB indicator, an SRVCC based CSFBindicator, an enhanced CSFB indicator, or an enhanced CSFB possibleindicator.

For example, the second indication information may include a CSFBindicator field, or a CSFB indicator field and a UE capability field.The CSFB indicator field instructs the MME to hand over the UE from theLTE network to the circuit switching CS domain of the 2G or 3G networkfor the CSFB. The UE capability field represents that the UE supports ahandover from the LTE network to the PS domain of the 2G or 3G network.

The first indication information may include a CSFB indicator field, ora CSFB indicator field and a UE capability field. The CSFB indicatorfield instructs the base station in the 2/3G network to hand over the UEfrom the LTE network to the circuit switching CS domain of the 2G or 3Gnetwork for the CSFB. The UE capability field represents that the UEsupports a handover from the LTE network to the PS domain of the 2G or3G network.

For example:

a) when a target network is a UTRAN network, the eNodeB adds the secondindication information to a source RNC to target RNC transparentcontainer; a CSFB information field in an existing source RNC to targetRNC transparent container may be used as a CSFB indicator field; and onefield may be added in the source RNC to target RNC transparent containerand is used as the UE capability field; and

b) when the target network is a GERAN network, the eNodeB adds thesecond indication information in old BSS to new BSS information; a CSFBindicator field or a UE capability field may be added in the old BSS tonew BSS information.

S5115: The MME sends a first handover request message to the MSC, wherethe first handover request message is used for requesting an MSC to handover the UE from the LTE network to the circuit switching CS domain ofthe second generation 2G or third generation 3G network for the CSFB.

Because the first handover request message is sent by the MME to theMSC, a handover required by the first handover request message is ahandover from the LTE network to the CS domain of the 2G or 3G network,that is, the first handover request is a handover request from PS to CS.

The first handover request message may carry third indicationinformation, where the third indication information is used forrequesting the MSC to hand over the UE from the LTE network to the CSdomain of the 2G or 3G network for the CSFB, that is, the thirdindication information represents that the first handover request issent for the CSFB. The third indication information may further indicatethat the UE supports a handover from the LTE network to the CS domain ofthe 2G or 3G network. The first handover request message may also notindicate the CSFB, and in this case, the MSC considers by default thatthe first handover request is sent for the CSFB.

When the MME receives the capability information of the UE from theeNodeB, the first handover request message may carry the capabilityinformation of the UE, for example, the capability information is atleast one of a class mark classmark 2 and a class mark classmark3.

Because the UE does not support a handover from the LTE network to theCS domain of the 2G or 3G network, the UE may not report voice codecinformation supported by the UE, and in this case, the MME may includedefault voice codec information in the first handover request messageaccording to a target system of the handover.

The third indication information in the first handover request messagemay be referred to as a CSFB indicator, an optimized CSFB indicator, aSRVCC based CSFB indicator, an enhanced CSFB indicator, or an enhancedCSFB possible indicator.

When the first handover request message carries a session transfernumber-single radio (Session Transfer Number-Single Radio, STN-SR), theMSC ignores the STN-SR number.

S5120: The MME sends a second handover request message to an SGSN, wherethe second handover request message is used for requesting the SGSN toinitiate a handover from the LTE network to a packet switching PS domainof the 2G or 3G network.

When the UE hands over from the LTE network to the CS domain, the UE maysimultaneously hand over to the PS domain, or may also notsimultaneously hand over to the PS domain. In this way, dependence ofthis solution on a network can be reduced, that is, it is only requiredthat an operator supports a handover from the LTE to the CS domain ofthe 2G or 3G network, and the operator does not need to support ahandover from the LTE to the PS domain of the 2G or 3G network.

S5121: The MSC sends a third handover request message to abase station,where the third handover request message is used for requesting the basestation to allocate a CS domain resource to the UE for handing over tothe CS domain of the 2G or 3G network;

The third handover request message is further used for requesting thebase station to hand over the user equipment UE from the Long TermEvolution LTE network to the circuit switching CS domain of the 2G or 3Gnetwork for the CSFB. The base station allocates the CS domain resourceto the UE for handing over from the LTE network to the CS domain of the2G or 3G network. For example, the CS domain resource allocated by thebase station includes a wired resource between the base station and theMSC and a wireless resource between the base station and the UE.

For example, the third handover request message includes fifthindication information, where the fifth indication information is usedfor requesting the base station to hand over the UE from the LTE networkto the CS domain for the CSFB;

and/or, the fifth indication information is further used for indicatingthat the UE supports a handover from the LTE network to the CS domain ofthe 2G or 3G network.

The third handover request message includes a source to targettransparent container, and the source to target transparent containerincludes the fifth indication information.

When the first handover request message does not include the voice codecinformation supported by the UE, the MSC sets default voice codecinformation according to a type of the 2G or 3G network, where thedefault voice codec information may be included in the third handoverrequest message.

The third handover request message includes integrity protectioninformation and/or encryption information, so that the base stationsends a security mode command to the UE after receiving a handovercompletion message.

S5125: The base station sends a third handover request response messageto the MSC, where the third handover request response message includesinformation about a CS domain wireless resource, and the informationabout the CS domain wireless resource is used for the UE to hand overfrom the LTE network to the CS domain of the 2G or 3G network.

S5130: The MSC sends a first handover response message to the MME, wherethe first handover response message includes the information about theCS domain wireless resource.

S135 a: The MME sends a handover required response message to theeNodeB, where the handover required response message includes theinformation about the CS domain wireless resource.

S135 b: The eNodeB sends a handover command to the UE, where thehandover command includes the information about the CS domain wirelessresource.

For example, the handover command includes fourth indicationinformation, where the fourth indication information is used forinstructing the UE to hand over from the LTE network to the CS domain ofthe 2G or 3G network for the CSFB.

For example, the handover command further includes information about aPS domain resource, and the UE hands over from the LTE network to the PSdomain of the 2G or 3G network according to the information about the PSdomain resource.

The handover command may further be used for instructing the UE to handover from the LTE network to the PS domain of the 2G or 3G network.

S5140: The UE hands over from the LTE network to the CS domain of the 2Gor 3G network according to the handover command.

The UE hands over, by using the resource information included in thehandover command, from the LTE network to the CS domain of the 2G or 3Gnetwork for the CSFB.

The UE generates a third session in a process of handing over from theLTE network to the CS domain of the 2G or 3G network. The UE may alsonot generate a session in a process of handing over from the LTE networkto the CS domain of the 2G or 3G network.

When the resource information includes a CS encryption algorithmidentifier, the UE activates CS domain encryption according to the CSencryption algorithm identifier in a process of handing over from theLTE network to the 2G network or 3G network.

S5145: After completing handover, the UE sends a handover completionmessage to the base station (the BSC or the RNC).

After receiving the handover completion message, in response to thehandover completion message, the base station needs to include alocation area identity (LAI) in UTRAN mobility information sent by theUE, which may cause that the UE initiates location area update (LAU) inthis embodiment, thereby causing that setup of a CS call fails. In orderto avoid the failure, the base station may not include the location areaidentity in the UTRAN mobility information sent by the UE.

The base station may send the LAI to the UE when sending the UTRANmobility information in a subsequent process, for example, the followingmethod may be used:

a) after receiving the handover completion message, the base stationstarts a timer, and after the timer expires, the base station sends theUTRAN mobility information, and sends the LAI to the UE; or,

b) when receiving a call IU release command or a call connectioncompletion (Connect) message, the base station sends the UTRAN mobilitymessage, and sends the LAI to the UE, where, for a calling party, theMSC sends a call connection completion (Connect) message to the UE; andfor a called party, the UE sends a call connection completion (Connect)message to the MSC.

Alternatively, when the UE sends an LAU message to the base station, toavoid a failure, the base station does not send the location updaterequest message to the MSC, and the base station directly sends alocation update acceptation message to the UE.

S5150: The base station forwards the handover completion message in stepS145 to the MSC.

S5155: The UE sends a connection management service request to the MSC.

S5160: The MSC sends an authenticate request to the UE.

Step S160 may also not be performed, that is, the MSC does not send theauthenticate request message to the UE.

S5165: The UE sends an authenticate response to the MSC.

S5170: The MSC sends a security mode command to the base station, wherethe security mode command carries integrity protection informationand/or encryption information, so that the base station sends thesecurity mode command to the UE.

Step S170 may also not be performed, that is, the MSC does not send thesecurity mode command to the base station.

S5175: The base station sends the security mode command to the UE.Specifically, the base station performs this step according to thesecurity mode command in step S170, or the base station performs thisstep after receiving the message in S145.

S5180: Optionally, the MSC sends a connection management serviceacceptation command (CM service Accept) to the UE.

S5185: The UE sends a first CS call connection setup request message(Setup) to the MSC, where the first CS call connection setup requestmessage is used for requesting the MSC to generate a first session forthe CSFB, or, the first CS call connection setup request message is usedfor requesting the MSC to generate a third session for the CSFB.

S5190: After receiving the first CS call connection setup requestmessage, if the first CS call setup request message is used forrequesting the MSC to generate the first session for the CSFB, the MSCsends a first session release message to the UE, where the first sessionrelease message is used for requesting the UE to release the thirdsession that is generated by the UE in a process of handing over fromthe LTE network to the CS domain of the 2G or 3G network.

If the first CS call connection setup request message is used forrequesting the MSC to generate the third session for the CSFB, the MSCdoes not need to send the first session release message to the UE.

S5195: The MSC calls a peer end.

S5196: The MSC sends an alerting (Alerting) message to the UE. The UEwaits for a response message from the peer end.

Further, the called party picks up, and a conversation state is entered.

After the call ends, because the call is triggered by the CSFB, the UEneeds to return to the LTE network after completing the call. The basestation determines, according to the third handover request message,that the call is triggered by the CSFB, and after receiving a callrelease message sent by the MSC, the base station in the 2G/3G networkredirects the UE to the LTE network, or, the base station hands over theUE to the LTE network, where the call release message is a releasecommand Iu Release Command or a clear command Clear Command.

It should be noted that, in this embodiment, the base station may parseCS signaling between the UE and the MSC. The base station receives asignaling message that is sent by the UE to the MSC, for example, aconnection management service request, an authenticate response, or afirst CS call connection setup request message. The base station maysend the signaling message to the MSC by using a connection that is setup in a process of handing over from the LTE network to the CS domain ofthe 2G or 3G network, or send the signaling message to the MSC by usinga direct transmission message.

In this embodiment, the indication information, the first indicationinformation, the second indication information, the third indicationinformation, the fourth indication information, and the fifth indicationinformation that are included in the notification message may include aCSFB indicator field, or a CSFB indicator field and a UE capabilityfield. The CSFB indicator field instructs the MME or the MSC or the basestation in the 2/3G network to hand over the UE from the LTE network tothe circuit switching CS domain of the 2G or 3G network for the CSFB.The UE capability field represents that the UE supports a handover fromthe LTE network to the PS domain of the 2G or 3G network.

In FIG. 1, in a circuit switched fallback implementation process, ahandover from an LTE network to a 2G or 3G network is triggered, so thatUE can directly hand over from the LTE network to a CS domain of the 2Gor 3G network. In this way, a resource may be allocated on a networkside to the UE for handing over from the LTE to the CS domain of the 2Gor 3G network, which avoids that a CS domain resource is allocated forthe CSFB after the UE hands over from the LTE network to a PS domain ofthe 2G or 3G network or is redirected to the 2G or 3G network, therebyreducing an access delay when the UE accesses the CS domain of the 2G or3G network.

Referring to FIG. 2, FIG. 2 shows a network handover process and acalled process after the network handover according to an embodiment ofthe present disclosure.

S0 b to S0 c: An MSC sends a CS paging request to an MME, and the MMEtriggers a paging process.

Steps S200 to S250 are the same as steps S100 to S150 in FIG. 1, anddetails are not described herein again.

S5255: UE sends a paging response to the MSC.

S5260: The MSC sends an authenticate request to the UE.

Step S260 may also not be performed, that is, the MSC does not send theauthenticate request message to the UE.

S5265: The UE sends an authenticate response to the MSC.

S5270: The MSC sends a security mode command to the base station, wherethe security mode command carries integrity protection informationand/or encryption information, so that the base station sends thesecurity mode command to the UE.

Step S270 may also not be performed, that is, the MSC does not send thesecurity mode command to the base station.

S5275: The base station sends the security mode command to the UE.Specifically, the base station performs this step according to thesecurity mode command in step S270, or the base station performs thisstep after receiving the message in S245.

S5280: The MSC sends a second CS call connection setup request messageto the UE, where the second CS call connection setup request message isused for requesting the UE to generate a second session for the CSFB,or, the second CS call connection setup request message is used forrequesting the UE to generate a third session for the CSFB.

After a step of receiving, by the UE, the second CS call connectionsetup request message sent by the mobile switching center MSC, themethod further includes:

receiving or sending, by the UE, session data of the second session byusing the resource.

S5285: The MSC receives a call confirmation message sent by the UE.

S5290: If the second CS call connection setup request message is usedfor requesting the UE to generate the second session for the CSFB, theMSC sends a second session release message to the UE, where the secondsession release message is used for requesting the UE to release thethird session that is generated by the UE in a process of handing overfrom the LTE network to the CS domain of the 2G or 3G network.

If the second CS call connection setup request message is used forrequesting the UE to generate the third session for the CSFB, the MSCdoes not need to send the second session release message to the UE.

The UE receives the session release message sent by the MSC.

S5295: The MSC sends an alerting message to the UE. The UE enters aconversation state.

S5296: The MSC triggers alerting of a peer end.

After the call ends, because the call is triggered by the CSFB, the UEneeds to return to the LTE network after completing the call. The basestation determines, according to the third handover request message,that the call is triggered by the CSFB; therefore, after receiving acall release message sent by the MSC, the base station in the 2G/3Gnetwork redirects the UE to the LTE network, or, the base station handsover the UE to the LTE network, where the call release message is arelease command Iu Release Command or a clear command Clear Command.

It should be noted that, in this embodiment, the base station may parseCS signaling between the UE and the MSC. The base station receives asignaling message that is sent by the UE to the MSC, for example, a callconfirmation message, an authenticate response, or a second CS callconnection setup request message. The base station may send thesignaling message to the MSC by using a connection that is set up in aprocess of handing over from the LTE network to the CS domain of the 2Gor 3G network, or send the signaling message to the MSC by using adirect transmission message.

In this embodiment, the indication information, the second indicationinformation, the third indication information, the fourth indicationinformation, and the fifth indication information that are included inthe notification message may include a CSFB indicator field, or a CSFBindicator field and a UE capability field. The CSFB indicator fieldinstructs the MME to hand over the UE from the LTE network to thecircuit switching CS domain of the 2G or 3G network for the CSFB. The UEcapability field represents that the UE supports a handover from the LTEnetwork to the PS domain of the 2G or 3G network.

In this embodiment of the present disclosure, in a circuit switchedfallback implementation process, a handover from an LTE network to a 2Gor 3G network is triggered, so that UE can directly hand over from theLTE network to a CS domain of the 2G or 3G network. In this way, aresource may be allocated on a network side to the UE for handing overfrom the LTE to the CS domain of the 2G or 3G network, which avoids thata CS domain resource is allocated for the CSFB after the UE hands overfrom the LTE network to a PS domain of the 2G or 3G network or isredirected to the 2G or 3G network, thereby reducing an access delaywhen the UE accesses the CS domain of the 2G or 3G network, shorteningentire voice call duration, and improving user experience.

In the foregoing two application scenarios, an entire network handoverand session process is described from two aspects: UE is a calling partyand UE is a called party.

Referring to FIG. 3, an embodiment of a network handover method providedin an embodiment of the present disclosure includes:

101: A mobility management entity MME receives a request messageinitiated by user equipment UE located in a Long Term Evolution LTEnetwork, where the request message is used for requesting circuitswitched fallback CSFB.

The request message may be an extended service request message.

102: The MME sends a notification message to an evolved base stationeNodeB according to the request message, where the notification messageis used for instructing the eNodeB to move the UE from the LTE networkto a circuit switching CS domain of a 2G or 3G network for the CSFB.

103: The MME receives a handover required message sent by the eNodeB.

104: The MME sends a first handover request message to a mobileswitching center MSC, where the first handover request message is usedfor requesting the MSC to hand over the UE from the LTE network to theCS domain of the 2G or 3G network for the CSFB, so that the 2G or 3Gnetwork allocates a CS domain resource to the UE, where the CS domainresource is used for the UE to hand over from the LTE network to the CSdomain of the 2G or 3G network.

For detailed descriptions of the foregoing processing steps and otherprocessing steps of the MME in this embodiment, reference may be made todescriptions of the embodiment corresponding to FIG. 1 or FIG. 2, anddetails are not described herein again.

Referring to FIG. 4, another embodiment of a network handover methodprovided in an embodiment of the present disclosure includes:

201: An evolved base station eNodeB located in a Long Term Evolution LTEnetwork receives a notification message sent by a mobility managemententity MME, where the notification message is used for instructing theeNodeB to move user equipment from the LTE network to a circuitswitching CS domain of a 2G or 3G network for circuit switched fallbackCSFB.

202: The eNodeB sends a handover required message to the MME.

203: The eNodeB receives a handover required response message sent bythe MME, where the handover required response message includesinformation about a CS domain wireless resource, and the informationabout the CS domain wireless resource is used for the UE to hand overfrom the LTE network to the CS domain of the 2G or 3G network.

204: The eNodeB sends a handover command to the UE, where the handovercommand is used for instructing the UE to hand over from the LTE networkto the CS domain of the 2G or 3G network, and the handover commandincludes the information about the CS domain wireless resource.

For detailed descriptions of the foregoing processing steps and otherprocessing steps of the evolved base station in this embodiment,reference may be made to descriptions of the embodiment corresponding toFIG. 1 or FIG. 2, and details are not described herein again.

Referring to FIG. 5, another embodiment of a network handover methodprovided in an embodiment of the present disclosure includes:

301: A mobile switching center MSC receives a first handover requestmessage sent by a mobility management entity MME, where the firsthandover request message is used for requesting the MSC to hand overuser equipment UE from an LTE network to a circuit switching CS domainof a second generation 2G or third generation 3G network for circuitswitched fallback CSFB.

302: The MSC sends a third handover request message to a base station inthe 2G or 3G network, where the third handover request message is usedfor requesting the base station to allocate a CS domain resource to theUE for handing over to the CS domain of the 2G or 3G network.

303: The MSC receives a third handover request response message sent bythe base station, where the third handover request response messageincludes information about a CS domain wireless resource that isallocated by the base station to the UE for handing over to the CSdomain of the 2G or 3G network.

304: The MSC sends a first handover response message to the MME, wherethe first handover response message includes the information about theCS domain wireless resource.

305: The MSC receives a handover completion message sent by the UE,where the handover completion message is used for indicating that the UEcompletes handing over from the LTE network to the CS domain of the 2Gor 3G network.

The method in this embodiment may further include the following step:

receiving, by the MSC, a first CS call connection setup request messagesent by the UE, where the first CS call connection setup request messageis used for requesting the MSC to generate a first session for the CSFB,where this step is a calling process of the UE.

The method in this embodiment may further include the following step:sending, by the MSC, a second CS call connection setup request messageto the UE, where the second CS call connection setup request message isused for requesting the UE to generate a second session for the CSFB,where this step is a called process of the UE.

For detailed descriptions of the foregoing processing steps and otherprocessing steps of the UE in this embodiment, reference may be made todescriptions of the embodiment corresponding to FIG. 1 or FIG. 2, anddetails are not described herein again.

Referring to FIG. 6, another embodiment of a network handover methodprovided in an embodiment of the present disclosure includes:

401: User equipment UE located in a Long Term Evolution LTE networksends a request message to a mobility management entity MME, where therequest message is used for requesting circuit switched fallback CSFB.

The request message may be an extended service request.

402: The UE receives a handover command sent by an evolved base stationeNodeB, where the handover command is used for instructing the UE tohand over from the LTE network to a circuit switching CS domain of a 2Gor 3G network for the CSFB, and the handover command includesinformation about a CS domain wireless resource that is allocated by the2G or 3G network to the UE for handing over from the LTE network to thecircuit switching CS domain of the 2G or 3G network.

403: The UE hands over from the LTE network to the CS domain of the 2Gor 3G network according to the handover command.

The method shown in FIG. 6 may further include:

sending, in the CS domain by the UE, a first CS call connection setuprequest message to a mobile switching center MSC, where the first CScall connection setup request message is used for requesting the MSC togenerate a first session for the CSFB, where this step is a callingprocess.

The method shown in FIG. 6 may further include: receiving, in the CSdomain by the UE, a second CS call connection setup request message sentby the MSC, where the second CS call connection setup request message isused for requesting the UE to generate a second session for the CSFB,where this step is a called process.

For detailed descriptions of the foregoing processing steps and otherprocessing steps of the UE in this embodiment, reference may be made todescriptions of the embodiment corresponding to FIG. 1 or FIG. 2, anddetails are not described herein again.

Referring to FIG. 7, another embodiment of a network handover methodprovided in an embodiment of the present disclosure includes:

S501: A base station in a 2G or 3G network receives a third handoverrequest message sent by a mobile switching center MSC, where the thirdhandover request message is used for requesting the base station to handover user equipment UE from a Long Term Evolution LTE network to acircuit switching CS domain of the 2G or 3G network for circuit switchedfallback CSFB.

S502: The base station sends a third handover request response messageto the MSC, where the third handover request response message includesinformation about a CS domain wireless resource, and the informationabout the CS domain wireless resource is used for the UE to hand overfrom the LTE network to the CS domain of the 2G or 3G network.

S503: The base station receives a handover completion message sent bythe UE, where the handover completion message is used for indicatingthat the UE completes handing over from the LTE network to the CS domainof the 2G or 3G network.

For detailed descriptions of the foregoing processing steps and otherprocessing steps of the base station in the 2G or 3G network in thisembodiment, reference may be made to descriptions of the embodimentcorresponding to FIG. 1 or FIG. 2, and details are not described hereinagain.

Referring to FIG. 8, a mobility management entity MME 60 provided in anembodiment of the present disclosure includes a receiving unit 601, agenerating unit 602, and a sending unit 603.

The receiving unit 601 is configured to receive a request messageinitiated by user equipment UE located in a Long Term Evolution LTEnetwork, where the request message is used for requesting circuitswitched fallback CSFB.

The generating unit 602 is configured to generate a notification messageaccording to the request message received by the receiving unit 601,where the notification message is used for instructing an evolved basestation eNodeB to move the UE from the LTE network to a circuitswitching CS domain of a second generation 2G or third generation 3Gnetwork for the CSFB.

The sending unit 603 is configured to send the notification messagegenerated by the generating unit 602 to the eNodeB.

The receiving unit 601 is further configured to receive a handoverrequired message sent by the eNodeB.

The generating unit 602 is further configured to generate a firsthandover request message according to the handover required messagereceived by the receiving unit 601, where the first handover requestmessage is used for requesting an MSC to hand over the UE from the LTEnetwork to the CS domain of the 2G or 3G network for the CSFB.

The sending unit 603 is further configured to send the first handoverrequest message generated by the generating unit to the mobile switchingcenter MSC, so that the 2G or 3G network allocates a CS domain resourceto the UE, where the CS domain resource is used for the UE to hand overfrom the LTE network to the CS domain of the 2G or 3G network.

The mobility management entity 60 may further include a determining unit604.

The determining unit 604 is configured to determine that the LTE networkand the 2G or 3G network support handing over the UE from the LTEnetwork to the CS domain of the 2G or 3G network for the CSFB, and thatthe UE supports a handover from the LTE network to the CS domain of the2G or 3G network.

The receiving unit 601 is further configured to receive a first handoverresponse message that is sent by the MSC in response to the firsthandover request message, where the first handover response messageincludes information about a CS domain wireless resource allocated tothe UE by a base station in the 2G or 3G network.

The generating unit 602 is further configured to generate a handoverrequired response message according to the handover required messagereceived by the receiving unit, where the handover required responsemessage includes the information about the CS domain wireless resource,and the information about the CS domain wireless resource is used forthe UE to hand over from the LTE network to the CS domain of the 2G or3G network for the CSFB. The sending unit 603 is further configured tosend the handover required response message to the eNodeB.

The mobility management entity in this embodiment may perform the stepsof the method of the MME described in the method embodiments of FIG. 1,FIG. 2, and FIG. 3, where the receiving unit 601 is configured toreceive a message that is sent by another entity to the MME, and thesending unit 602 is configured to send a message to another entity. Aperson skilled in the art may understand, according to the stepsperformed in the method embodiments, a relationship between behaviorsand performed actions of each unit in the MME and between the units.

Referring to FIG. 9, an evolved base station 70 provided in anembodiment of the present disclosure includes a receiving unit 701, agenerating unit 702, and a sending unit 703.

The receiving unit 701 is configured to receive a notification messagesent by a mobility management entity MME, where the notification messageis used for instructing the eNodeB to move user equipment UE from a LongTerm Evolution LTE network to a circuit switching CS domain of a 2G or3G network for circuit switched fallback CSFB.

The generating unit 702 is configured to generate a handover requiredmessage according to the notification message received by the receivingunit 701.

The sending unit 703 is configured to send the handover required messagegenerated by the generating unit 702 to the MME.

The receiving unit 701 is further configured to receive a handoverrequired response message sent by the MME, where the handover requiredresponse message includes information about a CS domain wirelessresource, and the information about the CS domain wireless resource isused for the UE to hand over from the LTE network to the CS domain ofthe 2G or 3G network.

The generating unit 702 is further configured to generate a handovercommand according to the handover required response message received bythe receiving unit 701, where the handover command is used forinstructing the UE to hand over from the LTE network to the CS domain ofthe 2G or 3G network, and the handover command includes the informationabout the CS domain wireless resource.

The sending unit 703 is further configured to send the handover commandgenerated by the generating unit 702 to the UE.

The evolved base station in FIG. 9 may further include a firstdetermining unit 704 and a second determining unit 705.

The first determining unit 704 is configured to determine that the UEsupports a handover from the LTE network to the CS domain of the 2G or3G network.

The second determining unit 705 is configured to determine that the UEsupports a handover from the LTE network to a PS domain of the 2G or 3Gnetwork.

When a handover required is a handover required of a handover from theLTE network to the CS domain and the PS domain of the 2G or 3G network,the handover command is further used for instructing the UE to hand overfrom the LTE network to the PS domain of the 2G or 3G network, where thehandover command includes information about a PS domain resource of the2G or 3G network, and the information about the PS domain resource isused for the UE to hand over from the LTE network to the PS domain ofthe 2G or 3G network.

The evolved base station in this embodiment may perform the steps of themethod of the evolved base station described in the method embodimentsof FIG. 1, FIG. 2, and FIG. 4, where the receiving unit 701 isconfigured to receive a message that is sent by another entity to theevolved base station, and the sending unit 702 is configured to send amessage to another entity. A person skilled in the art may understand,according to the steps performed in the method embodiments, arelationship between behaviors and performed actions of each unit in theevolved base station and between the units.

Referring to FIG. 10, a mobile switching center MSC 80 provided in anembodiment of the present disclosure includes a receiving unit 801, agenerating unit 802, and a sending unit 803.

The receiving unit 801 is configured to receive a first handover requestmessage sent by a mobility management entity MME, where the firsthandover request message is used for requesting the MSC to hand overuser equipment UE from an LTE network to a circuit switching CS domainof a second generation 2G or third generation 3G network for circuitswitched fallback CSFB.

The generating unit 802 is configured to generate a third handoverrequest message according to the first handover request message receivedby the receiving unit 801, where the third handover request message isused for requesting a base station in the 2G or 3G network to allocate aCS domain resource to the UE for handing over to the CS domain of the 2Gor 3G network.

The sending unit 803 is configured to send the third handover requestmessage generated by the generating unit 802 to the base station.

The receiving unit 801 is further configured to receive a third handoverrequest response message sent by the base station, where the thirdhandover request response message includes information about a CS domainwireless resource that is allocated by the base station to the UE forhanding over to the CS domain of the 2G or 3G network.

The generating unit 802 is further configured to generate a firsthandover response message according to the first handover requestmessage received by the receiving unit 801, where the first handoverresponse message includes the information about the CS domain wirelessresource.

The sending unit 803 is further configured to send the first handoverresponse message generated by the generating unit 802 to the MME.

The receiving unit 801 is further configured to receive a handovercompletion message sent by the UE, where the handover completion messageis used for indicating that the UE completes handing over from the LTEnetwork to the CS domain of the 2G or 3G network.

The receiving unit 801 is further configured to receive a first CS callconnection setup request message sent by the UE, where the first CS callconnection setup request message is used for requesting the MSC togenerate a first session.

The sending unit 803 is further configured to send a second CS callconnection setup request message to the UE, where the second CS callconnection setup request message is used for requesting the UE togenerate a second session.

The sending unit 803 is further configured to: after the receiving unitreceives the first CS call connection setup request message, send asession release message to the UE, where the session release message isused for requesting the UE to release a third session that is generatedby the UE in a process of handing over from the LTE network to the CSdomain of the 2G or 3G network.

The sending unit 803 is further configured to: after the receiving unitreceives the call confirmation message, send a session release messageto the UE, where the session release message is used for requesting theUE to release a third session that is generated by the UE in a processof handing over from the LTE network to the CS domain of the 2G or 3Gnetwork.

The MSC in this embodiment may perform the steps of the method of theMSC described in the method embodiments of FIG. 1, FIG. 2, and FIG. 5,where the receiving unit 801 is configured to receive a message that issent by another entity to the MSC, and the sending unit 802 isconfigured to send a message to another entity. A person skilled in theart may understand, according to the steps performed in the methodembodiments, a relationship between behaviors and performed actions ofeach unit in the MSC and between the units.

Referring to FIG. 11, user equipment 90 provided in an embodiment of thepresent disclosure includes: a sending unit 901, a receiving unit 902,and a handover unit 903.

The sending unit 901 is configured to send a request message to amobility management entity MME, where the request message is used forrequesting circuit switched fallback CSFB.

The receiving unit 902 is configured to receive a handover command sentby an evolved base station eNodeB, where the handover command is usedfor instructing the UE to hand over from a Long Term Evolution LTEnetwork to a circuit switching CS domain of a 2G or 3G network for theCSFB, and the handover command includes information about a CS domainwireless resource that is allocated by the 2G or 3G network to the UEfor handing over from the LTE network to the CS domain of the 2G or 3Gnetwork.

The handover unit 903 is configured to hand over from the LTE network tothe CS domain of the 2G or 3G network according to the resourceinformation received by the receiving unit 902.

The sending unit 901 is further configured to send, in the CS domain ofthe 2G or 3G network, a first CS call connection setup request messageto a mobile switching center MSC, where the first CS call connectionsetup request message is used for requesting the MSC to generate a firstsession.

The receiving unit 902 is further configured to receive, in the CSdomain of the 2G or 3G network, a second CS call connection setuprequest message sent by the mobile switching center MSC, where thesecond CS call connection setup request message is used for requestingthe UE to generate a second session.

The receiving unit 902 is further configured to receive a sessionrelease message sent by the MSC, where the session release message isused for instructing the UE to release a third session that is generatedby the UE in a process of handing over from the LTE network to the CSdomain of the 2G or 3G network.

The UE in this embodiment may perform the steps of the method of the UEdescribed in the method embodiments of FIG. 1, FIG. 2, and FIG. 6, wherethe receiving unit 901 is configured to receive a message that is sentby another entity to the UE, and the sending unit 902 is configured tosend a message to another entity. A person skilled in the art mayunderstand, according to the steps performed in the method embodiments,a relationship between behaviors and performed actions of each unit inthe UE and between the units.

Referring to FIG. 12, abase station 100 in a second generation 2G orthird generation 3G network provided in an embodiment of the presentdisclosure includes: a receiving unit 1001, a generating unit 1002, anda sending unit 1003.

The receiving unit 1001 is configured to receive a third handoverrequest message sent by a mobile switching center MSC, where the thirdhandover request message is used for requesting the base station to handover user equipment UE from a Long Term Evolution LTE network to acircuit switching CS domain of the 2G or 3G network for circuit switchedfallback CSFB.

The generating unit 1002 is configured to generate a third handoverrequest response message according to the third handover request messagereceived by the receiving unit 1001, where the third handover requestresponse message includes information about a CS domain wirelessresource, and the information about the CS domain wireless resource isused for the UE to hand over from the LTE network to the CS domain ofthe 2G or 3G network.

The sending unit 1003 is configured to send the third handover requestresponse message generated by the generating unit 1002 to the MSC.

The receiving unit 1001 is further configured to receive a handovercompletion message sent by the UE, where the handover completion messageis used for indicating that the UE completes handing over from the LTEnetwork to the CS domain of the 2G or 3G network.

The sending unit 1003 is further configured to send Universal MobileTelecommunications System terrestrial radio access network UTRANmobility information to the UE, where the UTRAN mobility informationdoes not include a location domain identity LAI, and after apredetermined time, send the LAI to the UE.

The sending unit 1003 is further configured to send the Universal MobileTelecommunications System terrestrial radio access network UTRANmobility information to the UE, where the UTRAN mobility informationdoes not include a location domain identity LAI.

The receiving unit 1001 is further configured to receive a call releasecommand or call connection completion message sent by the MSC or a callconnection completion message sent by the UE.

The sending unit 1003 is further configured to send the LAI to the UEafter the receiving unit receives the call release command or the callconnection completion message.

The receiving unit 1001 is further configured to receive a locationupdate request message sent by the UE, and determine to skip sending thelocation update request message to the MSC.

The sending unit 1003 is further configured to send a location updateacceptation message to the UE after the receiving unit 1001 receives thelocation update request message.

The receiving unit 1001 is further configured to receive a call releasemessage sent by the MSC, where the call release message is an Iuinterface release command or a clear command.

The base station 100 further includes a redirection unit 1004 or ahandover unit 1005.

The redirection unit 1004 is configured to redirect the UE to the LTEnetwork according to the call release message received by the receivingunit 1001.

The handover unit 1005 is configured to hand over the UE to the LTEnetwork according to the call release message received by the receivingunit 1001.

The base station in this embodiment may perform the steps of the methodof the base station described in the method embodiments of FIG. 1, FIG.2, and FIG. 7, where the receiving unit 1001 is configured to receive amessage that is sent by another entity to the base station, and thesending unit 1002 is configured to send a message to another entity. Aperson skilled in the art may understand, according to the stepsperformed in the method embodiments, a relationship between behaviorsand performed actions of each unit in the base station and between theunits.

In the apparatus embodiments of the present disclosure, in a circuitswitched fallback implementation process, a handover from an LTE networkto a 2G or 3G network is triggered, so that UE can directly hand overfrom the LTE network to a CS domain of the 2G or 3G network. In thisway, a resource may be allocated on a network side to the UE for handingover from the LTE to the CS domain of the 2G or 3G network, which avoidsthat a CS domain resource is allocated for the CSFB after the UE handsover from the LTE network to a PS domain of the 2G or 3G network or isredirected to the 2G or 3G network, thereby reducing an access delaywhen the UE accesses the CS domain of the 2G or 3G network, shorteningentire voice call duration, and improving user experience.

A person skilled in the art can understand that, in the embodiments ofFIG. 8 to FIG. 12, the sending unit configured to send a message may beimplemented by using a transmitter, and the receiving unit configured toreceive a message may be implemented by using a receiver. Alternatively,the sending unit and the receiving unit both can be implemented by usinga transceiver. In physical implementation, the transmitter or thetransceiver may be implemented by using one physical entity, or may alsobe implemented by using multiple physical entities, and the transmitterand the transceiver maybe implemented by using one physical entity, ormay also be implemented by using multiple physical entities, which willnot be limited in the present disclosure. Other units, such as thegenerating unit, an allocation unit, the redirection unit, the handoverunit, and the determining unit, may be implemented by using one or moreprocessors, which will not be limited in the present disclosure.

Referring to FIG. 13, an embodiment of a network handover systemprovided in an embodiment of the present disclosure includes: themobility management entity 60, the evolved base station 70, the mobileswitching center 80, the base station 100, and the user equipment 90.

For actions performed by the mobility management entity 60, the evolvedbase station 70, the mobile switching center 80, the base station 100,and the user equipment 90 and interaction therebetween, reference may bemade to descriptions in FIG. 1 and FIG. 2, and descriptions of themethod embodiments and the apparatus embodiments in FIG. 3 to FIG. 12,and details are not described herein again.

A person of ordinary skill in the art may be aware that, in combinationwith the examples described in the embodiments disclosed in thisspecification, units and algorithm steps may be implemented byelectronic hardware, computer software, or a combination thereof. Toclearly describe the interchangeability between the hardware and thesoftware, the foregoing has generally described compositions and stepsof each example according to functions. Whether the functions areperformed by hardware or software depends on particular applications anddesign constraint conditions of the technical solutions. A personskilled in the art may use different methods to implement the describedfunctions for each particular application, but it should not beconsidered that the implementation goes beyond the scope of the presentdisclosure.

It may be clearly understood by a person skilled in the art that, forthe purpose of convenient and brief description, for a detailed workingprocess of the foregoing system, apparatus, and unit, refer to acorresponding process in the foregoing method embodiments, and detailsare not described herein again.

In the several embodiments provided in the present application, itshould be understood that the disclosed system, apparatus, and methodmay be implemented in other manners. For example, the describedapparatus embodiment is merely exemplary. For example, the unit divisionis merely logical function division and may be other division in actualimplementation. For example, a plurality of units or components may becombined or integrated into another system, or some features may beignored or not performed. In addition, the displayed or discussed mutualcouplings or direct couplings or communication connections may beimplemented by using some interfaces. The indirect couplings orcommunication connections between the apparatuses or units may beimplemented in electronic, mechanical, or other forms.

The units described as separate parts may or may not be physicallyseparate, and parts displayed as units may or may not be physical units,maybe located in one position, or may be distributed on a plurality ofnetwork units. Some or all of the units may be selected according toactual needs to achieve the objectives of the solutions of theembodiments of the present disclosure.

In addition, functional units in the embodiments of the presentdisclosure may be integrated into one processing unit, or each of theunits may exist alone physically, or two or more units are integratedinto one unit. The integrated unit may be implemented in a form ofhardware, or may be implemented in a form of a software functional unit.

When the integrated unit is implemented in the form of a softwarefunctional unit and sold or used as an independent product, theintegrated unit may be stored in a computer-readable storage medium.Based on such an understanding, the technical solutions of the presentdisclosure essentially, or the part contributing to the prior art, orall or some of the technical solutions may be implemented in the form ofa software product. The software product is stored in a storage mediumand includes several instructions for instructing a computer device(which may be a personal computer, a server, or a network device) toperform all or some of the steps of the methods described in theembodiments of the present disclosure. The foregoing storage mediumincludes: any medium that can store program code, such as a USB flashdrive, a removable hard disk, a read-only memory (ROM), a random accessmemory (RAM), a magnetic disk, or an optical disc.

The LTE network described in the present disclosure includes an LTE Anetwork, and an LTE version that may exist subsequently.

The foregoing descriptions are merely specific embodiments of thepresent disclosure, but are not intended to limit the protection scopeof the present disclosure. Any modification or replacement readilyfigured out by a person skilled in the art within the technical scopedisclosed in the present disclosure shall fall within the protectionscope of the present disclosure. Therefore, the protection scope of thepresent disclosure shall be subject to the protection scope of theclaims.

What is claimed is:
 1. A network handover method, comprising: sending, by user equipment (UE) located in along term evolution (LTE) network, a request message to a mobility management entity (MME) for requesting circuit switched fallback (CSFB); receiving, by the UE, a handover command sent by an evolved base station (eNodeB) for instructing the UE to hand over from the LTE network to a circuit switching (CS) domain of a second generation (2G) or third generation (3G) network for the CSFB, and the handover command comprises information about a CS domain wireless resource that is allocated by the 2G or the 3G network to the UE for handing over from the LTE network to the CS domain of the 2G or 3G network; handing over, by the UE, from the LTE network to the CS domain of the 2G or the 3G network according to the handover command; receiving, by the UE, a session release message sent by the MSC for instructing the UE to release a third session that is generated by the UE in a process of handing over from the LTE network to the CS domain of the 2G or 3G network; wherein before receiving, by the UE, the session release message sent by the MSC, the method comprises one of the following steps: sending, in the CS domain of the 2G or 3G network by the UE, a CS call connection setup request message to a mobile switching center MSC for requesting the MSC to generate a first session; or sending, in the CS domain of the 2G or 3G network by the UE, a call confirmation message to the MSC, responding to a second CS call connection setup request message, wherein the CS call connection setup request message is used for requesting the UE to generate a second session.
 2. The method according to claim 1, wherein the handover command further comprises information about a packet switching (PS) domain wireless resource that is allocated by the 2G or 3G network to the UE for handing over from the LTE network to a PS domain of the 2G or 3G network.
 3. The method according to claim 1, further comprising: activating, by the UE, circuit switching (CS) domain encryption according to a CS encryption algorithm identifier included in the handover command in a process of handing over from the LTE network to the 2G network or 3G network.
 4. User equipment (UE), comprising: a transceiver; at least one processor; and a non-transitory computer-readable storage medium coupled to the at least one processor and storing programming instructions for execution by the processor, the programming instructions instruct the at least one processor to: send, through the transceiver, a request message to a mobility management entity (MME) for requesting circuit switched fallback (CSFB); receive, through the transceiver, a handover command sent by an evolved base station (eNodeB) for instructing the UE to hand over from a long term evolution (LTE) network to a circuit switching (CS) domain of a second generation (2G) or third generation (3G) network for the CSFB, and the handover command comprises information about a CS domain wireless resource that is allocated by the 2G or 3G network to the UE for handing over from the LTE network to the CS domain of the 2G or 3G network; hand over from the LTE network to the CS domain of the 2G or 3G network according to the handover command received by the receiving unit; send, through the transceiver, in the CS domain of the 2G or 3G network, a first CS call connection setup request message to a mobile switching center (MSC) for requesting the MSC to generate a first session, or send, in the CS domain of the 2G or 3G network, a call confirmation message to the MSC, responding to a second CS call connection setup request message, wherein the second CS call connection setup request message is used for requesting the UE to generate a second session; and receive, through the transceiver, a session release message sent by the MSC, wherein the session release message is used for instructing the UE to release a third session that is generated by the UE in a process of handing over from the LTE network to the CS domain of the 2G or 3G network.
 5. The UE according to claim 4, wherein the handover command further comprises information about a PS domain wireless resource that is allocated by the 2G or 3G network to the UE for handing over from the LTE network to a packet switching PS domain of the 2G or 3G network.
 6. The UE according to claim 4, wherein the programming instructions instruct the at least one processor to: activate CS domain encryption according to a CS encryption algorithm identifier included in the handover command in a process of handing over from the LTE network to the 2G network or 3G network.
 7. A non-transitory computer readable medium comprising computer program codes stored thereon, executable by one or more digital processors for providing system configurations, the computer program codes including: instructions for sending a request message to a mobility management entity (MME) for requesting circuit switched fallback (CSFB); instructions for receiving a handover command sent by an evolved base station (eNodeB) for instructing the UE to hand over from a long term evolution (LTE) network to a circuit switching (CS) domain of a second generation (2G) or third generation (3G) network for the CSFB, and the handover command comprises information about a CS domain wireless resource that is allocated by the 2G or 3G network to the UE for handing over from the LTE network to the CS domain of the 2G or 3G network; instructions for handing over from the LTE network to the CS domain of the 2G or the 3G network according to the handover command; instructions for sending in the CS domain of the 2G or 3G network, a first CS call connection setup request message to a mobile switching center (MSC) for requesting the MSC to generate a first session, or send, in the CS domain of the 2G or 3G network, a call confirmation message to the MSC, responding to a second CS call connection setup request message for requesting the UE to generate a second session; and instructions for receiving a session release message sent by the MSC for instructing the UE to release a third session that is generated by the UE in a process of handing over from the LTE network to the CS domain of the 2G or 3G network.
 8. The non-transitory computer readable medium according to claim 7, wherein: the handover command further comprises information about a packet switching (PS) domain wireless resource that is allocated by the 2G or the 3G network to the UE for handing over from the LTE network to a PS domain of the 2G or 3G network.
 9. The non-transitory computer readable medium according to claim 7, wherein the computer program codes include: instructions for activating CS domain encryption according to a CS encryption algorithm identifier included in the handover command in a process of handing over from the LTE network to the 2G network or the 3G network. 